Definition - What does Inert mean?
In horticulture, inert may refer to matter that is found in soil-less media, seed packages, fertilizers or pesticides. In general it relates to any material that is devoid of nutrients or active ingredients and are generally included to add structure, substance or as a carrier for the desired product. The percentage of inert matter in a horticultural product may also dictate its price or quality.
Some products such as certified seed are required by law to have established thresholds of inert material. With seeds, generally the less inert material, the higher the quality. In other instances, inert materials are critical for proper application rates such as with fertilizers or pesticides.
MaximumYield explains Inert
In commercial seed packets, inert material usually refers to any soil, leaf or plant matter or debris that may have been inadvertently collected along with the seeds. In soil-less mixes, it refers to the content of the media that doesn't provide any nutrition to the mix, but may add structure, water holding and nutrient holding capacity or give the mix weight so that plants may be less prone to getting knocked over once potted.
For pesticides and fertilizer, the inert material may just be filler to allow for more even distribution of the desired ingredients. In the case of aerosols, the inert material may be the propellant that the active ingredient is delivered by.